Compared with traditional LCD display mode, it is not necessary for OLED display technique to use backlights. The OLED display technique has the property of self-illumination, a very thin organic material film and a glass substrate are used, and the organic material can glow when an electric current passes through it. Therefore an OLED display can provide significant power savings, can be lighter and thinner, and can tolerate a wider range of temperature variation than LCDs, with a wider viewing angle. The light-emitting layer of the OLED screen is composed by organic light-emitting components formed on corresponding pixel locations on an array substrate by using evaporation film technology to organic materials through a fine metal mask. The OLED screen should be colorized for color display. The side-by-side mode has the best effect on colorized screen. In the side-by-side mode, there are red, green and blue (R, G and B) three sub pixels in a pixel, and every sub pixel has an independent light-emitting component. Because the organic light-emitting materials of red, green and blue three sub pixels are different, in the production process, it needs to evaporate three different kinds of organic materials to red, green and blue three-color light-emitting sub pixels on the corresponding locations by a metal mask, and the color-ratio of the combination of the three colors is adjusted to create true color. In this way, the red, green and blue constitute three-color OLED components emit light independently to form a pixel.
The production of the pixel per inch (PPI) OLED screen has focused on fine metal mask with good mechanical stability, and the key to the fine metal mask is the arrangement of pixels and sub pixels.
According to the arrangement of the pixel array, there are a few kinds of opening methods of the metal mask existing in industry as follows.
Slit Mode
FIG. 1 shows a traditional pixel arrangement arranged side by side. The light-emitting layer of the OLED display is composed by pixel cells 100 arranged on a substrate 10 in multi-row and multi-column. For the pixel arrangement as shown in FIG. 1, there are red (R) 102, green (G) 103 and blue (B) 100 three sub pixels parallel to each other in one pixel cell 100. In order to form the pixel arrangement, the corresponding metal mask is shown in FIG. 2.
FIG. 2 shows a metal mask used to form one of the sub pixels (R sub pixel) in the pixel structure as shown in FIG. 1 on the OLED display substrate. It will be appreciated that the rest sub pixels (G and B) can be formed by a metal mask having the same above structure due to each sub pixel having the same patterning.
The metal mask includes a metal substrate 20 and a rectangular opening 200 thereon. Wherein, the number of the opening can be determined by the number of the pixel required by the resolution of the OLED display. FIG. 2 shows four columns of openings 200. A section 201 between adjacent two openings 200 forms an unopened metal strip of the metal substrate 20. As shown in FIG. 1, the opening method of the metal mask is that one opening 200 is shared by all the sub pixels in the same column (for example, R sub pixels) in the OLED screen. Thus the opening 200 of the metal mask is relative long in length. With the increase in display size, the length of the opening of the metal mask needs to be increased.
This shows Slit Mode is easy to make and use the metal mask for low-resolution OLED screens due to which the number of pixels is small that the space between adjacent openings 200 is relative large, i.e., the width of the metal strip is relative wide.
However, the above opening mode needs a fine metal mask when used for a high resolution screen. The space between adjacent openings 200 is reduced for the increase in the number of pixels, i.e., the metal strip 201 is relative fine. This creates a problem that the metal strip is likely to be out of shape under the influence of magnetic field lines of the magnetic board during the use of the metal mask, resulting in color mixing caused by the spread of different color materials in among pixels, and resulting in low yield during production. Moreover, this kind of metal mask is easy to be damaged or deformed in the process of using, cleaning and storing, with a low repetitive use rate, and the screen produced by this mode has a high cost due to the high cost of the metal mask.
Slot Mode
In view of the above problem, a metal mask solution with a slot is provided, as shown in FIG. 3, to form the arrangement of pixels as shown in FIG. 1. As FIG. 3, the opening mode of the metal mask is that based on Slit Mode the locations corresponding to the spaces between the sub pixels as shown in FIG. 1 and corresponding to the openings 200 as shown in FIG. 2 are provided with metal bridges 301 connecting adjacent metal strips, so that one long opening 200 as show in FIG. 2 is changed into a plurality of openings units 300 corresponding to the sub pixel structure as shown in FIG. 1.
This opening mode makes the metal strip of the metal mask stronger to resolve the above problem that the metal strip is likely to be out of shape under the influence of magnetic field lines and external force in Slit Mode. However in view of the precision of long size of the metal mask that adequate distance must be maintained between the sub pixel and the bridge in order to avoid shadow effect in sub pixels when evaporation, the reduction in the length between bottoms of the sub pixel will affect the opening rate of every sub pixel.
To solve this problem, a U.S. patent No. 20110128262A1 discloses another pixel structure different from the above pixel structure, as shown in FIG. 4. The pixel structure includes a plurality of pixel units 400 arranged in multi-row and multi-column, each pixel is composed of red, green and blue three sub pixels, where the blue sub pixel has the largest surface area due to fastest attenuation of blue light, while the red and green sub pixels are arranged on one side of the blue sub pixel and respectively arranged on the upper and lower locations along the long side of the blue sub pixel.
The pixel units 400 are arranged repeatedly to form a pixels array. The arrangement of the pixel structure makes the spaces between the openings of the metal mask corresponding to the red and green sub pixels (as FIGS. 5-6) are relatively large that high-resolution display can be achieved to some extent.
However, the blue sub pixels in the pixel array are aligned as FIG. 1, so that their corresponding metal mask must use the opening mode as the above Slit or Slot (as FIG. 7). Because both the above Slit Mode and Slot Mode have defects, the opening mode of the blue metal mask (B mask) of the arrangement of the pixel array as shown in FIG. 4 seriously affects the opening rate of the sub pixel and the resolution further upgrade.